There may be different reasons to use SafeSpace: to remain protected from malware, to prevent access to your personal data while browsing the Internet or simply to try new applications without the risk of ruining your whole system configuration.
In any case, SafeSpace works as a kind of sandbox that enables you to launch applications, open files and download anything you want in a protected virtual environment that doesn't change or affect your system at all. You can select which applications can be launched in this safe mode, as well as the folders they'll have access to. The program displays a nicely designed interface and is very easy to use.
Just one more thing: in exchange for this extra security layer, you'll have to be patient because apps will be noticeably slower.